Conventionally, radiation thermometers of this kind calculate a temperature of an object being measured, on the basis of an output of a thermopile and a temperature of a thermopile chip, in accordance with the following formula of principleE=L(Tx4−Ta4)where E: energy (output of a thermopile chip) received by the thermopile chip, L: a coefficient, Tx: temperature of an object being measured, and Ta: temperature of the thermopile chip.
Also, sensors for measuring a radiant quantity of infrared rays include a thermopile sensor generally constructed such that a thermopile chip is bonded to a metallic stem, a window of silicone glass capable of transmitting therethrough infrared rays is provided on a roof panel, and the whole is sealed by a metallic casing.
With a thermometer making use of such thermopile sensor, as disclosed in JP-A-5-203499, a thermistor is bonded to a portion immediately laterally of a thermopile chip in the metallic casing or behind the thermopile chip with the metallic casing therebetween for the purpose of measuring a temperature of the thermopile chip, and a temperature of the thermistor is assumed to be equal to a temperature of the thermopile chip.
Also, the thermopile chip gives and receives energy in the form of infrared rays from all objects, which are disposed in front of the thermopile chip and different in temperature from the thermopile chip, and converts the energy into voltage to output the same.
Accordingly, a measurement of one thermistor is used and made a representative value of the thermopile sensor in the same manner as the above example, assuming that the thermopile sensor is made isothermal and the thermopile casing involves no temperature difference. While JP-A-2-35322 describes an example of measuring a temperature of a wave guide disposed in front of a thermopile sensor, it is premised on the assumption that a thermopile casing itself involves no temperature difference.
With radiation thermometers, in which a probe is inserted into an ear to measure a body temperature by the medium of infrared rays irradiated from an eardrum, however, heat is conducted to respective members, which constitute the probe, from an external auditory canal or the like to generate a temperature distribution on a-thermopile sensor itself when the probe is inserted into an ear at the time of measurement of body temperature. Such influences of heat from outside come out markedly, particularly in the case where the probe is inserted into an ear for a long time and the probe is repeatedly inserted into an ear. When a temperature difference is generated in a thermopile sensor itself and a temperature difference is generated between a thermopile casing disposed in front of a thermopile chip and the thermopile chip, the thermopile chip receives infrared rays from the thermopile casing in addition to infrared rays irradiated from an object (eardrum) being measured, whereby there is caused an error that a higher temperature than that of the actual object being measured is measured.
Also, as for the way of conduction of heat from outside, when a human body is an object being measured, an adult and a child are different in size and depth of earhole and in position and area, in which a probe contacts with an external ear, so that the way of conduction of heat to the probe is varied. Accordingly, errors generated are varied in amount depending upon whether an object being measured is an adult and a child. Further, that manner, in which a thermometer is influenced by heat in the case where temperature measurement is made by the use of a blackbody furnace or the like other than a human body for the purpose of proof of accuracy of the thermometer, is quite different from the case where a human body is an object being measured, and errors generated are naturally different in amount from the case where a human body is an object being measured. Accordingly, with thermometers for persons in a wide range, no correct measurement is obtained when differences in objects being measured are neglected and measurement errors caused by influences of heat from outside are uniformly corrected.
The invention has been thought of in order to solve such problems of the conventional art, and has its object to suppress measurement errors caused by influences of heat from outside, thereby enhancing accuracy in temperature measurement.